It discovered that seniors with osteoporosis who followed a Mediterranean-like diet for 12 months had a much slower rate of hip bone loss than peers who did not follow the diet.
Osteoporosis increases the risk of fracture by reducing bone mass and degenerating the structure of bone tissue.
Hip fracture is common in older people with osteoporosis.
This adds to a growing body of research on the many health benefits of the Mediterranean diet, which is rich in vegetables, fruits, nuts, fish, wholegrains, and olive oil.
A paper on the trial — which was led by the University of Bologna in Italy — is now published in the American Journal of Clinical Nutrition.
Reduced rate of bone loss
The year-long study randomly assigned over 1,000 volunteers, aged 65–79, living in France, Italy, the Netherlands, Poland, and the United Kingdom to one of two groups.
One group adopted a "Mediterranean-like diet" for the duration, and the other — the control group — did not.
The trial is the first to examine the effect of a Mediterranean diet on bone health in seniors across several European centers over this length of time.
The Mediterranean-like diet had little or no effect on the participants whose bone density was normal, but it did reduce the rate of bone loss in individuals with osteoporosis.
Commenting on the results, corresponding study author Susan J. Fairweather-Tait, a professor at the University of East Anglia's Norwich Medical School in the U.K., explains that a year isn't long compared with the time it takes for bone to form.
"So," she explains, "the fact [that] we were able to see a marked difference between the groups even in just this one area is significant."
Bones and osteoporosis
Bone is not a dead material, but a living tissue that can replenish itself. Its main components are the protein collagen and a mineral called calcium phosphate. Together, these make bones flexible, strong, and resilient.
Bone goes through a continuous cycle of resorption — during which old bone is taken away — and formation. From birth through adolescence and early adulthood, "formation outpaces resorption," and bones increase in size, weight, and density.
But at around the age of 30, bone density and strength peak, and bone mass begins to decline as resorption gradually outpaces formation.
Osteoporosis is a preventable and treatable disease that makes bones fragile and raises the risk of fracture in the hip, wrist, and spine.
It arises when the rate of resorption is too fast or formation is too slow and is more likely to occur in individuals who do not reach "optimal peak bone mass."
After menopause, the rate of bone loss speeds up in women, who account for about 80 percent of osteoporosis cases.
In the United States, there are more than 53 million people who either "already have osteoporosis" or are at a higher risk of developing it because of low bone mass.
Setting up the trial
The aim of the recent trial — which was funded by the European Union — was to test the effect of a Mediterranean diet on bone mineral density and markers of "bone and collagen degradation" in older Europeans.
The diet used in the trial featured: a high amount of fruits, vegetables, wholegrains, nuts, olive oil, and fish; small amounts of meat and dairy produce; and a moderate amount of alcohol.
Those in the group that followed a Mediterranean diet were given "individually tailored advice" on how to stick to the diet. They were also given food such as whole-grain pasta and olive oil, and a small dose of 10 micrograms of vitamin D-3 per day.
The authors note that the aim of supplementing the Mediterranean diet with a small amount of vitamin D-3 was to "even out" the variance in the effect that different amounts of sunshine might have in the different countries.
The participants in the control group did not receive any instructions, but they were given leaflets about how to eat healthfully that might be typically handed out in their country.
Three measures of bone density, as well as blood samples, were taken at the start and end of the study.
Reduced hip bone loss in osteoporosis
The findings showed that in the participants who had normal bone density, there was little effect on bone health measures from the diet.
Also, of the participants who had osteoporosis, there was the expected age-related decline in bone density in the control group.
Decline in bone density was also seen in two of the bone density measures — lumbar spine and whole-body — in the participants with osteoporosis in the Mediterranean diet group. However, there was an "equivalent increase" in bone density in the neck of the femur.
The neck of the femur is the top part of the thigh bone just before the ball-shaped end that fits in the socket of the hip joint.
"This is a particularly sensitive area for osteoporosis," Prof. Fairweather-Tait says, "as loss of bone in the femoral neck is often the cause of hip fracture, which is common in elderly people with osteoporosis."
Larger, longer studies needed
The authors believe that if the trial had lasted longer, they might have detected other diet-induced changes — including in the participants with normal bone density.
They call for longer, larger trials of people with osteoporosis to confirm their findings and establish whether the change of diet can also affect other bones.
In the meantime, the team sees "no reason" why anyone with concerns should not move toward a Mediterranean-like diet.
"A Mediterranean diet is already proven to have other health benefits, reducing the risk of cardiovascular disease, Parkinson's, Alzheimer's, and cancer."
Prof. Susan J. Fairweather-Tait